1. Field of the Invention
The present invention relates to a parallel hybrid (electric) vehicle having an engine and a motor/generator (a motor serving also as a generator), an output torque of either one or both of these engine and motor/generator being transmitted to a transmission via a torque synthesis mechanism so that a vehicular running driving force is obtained from either one or both of the engine and motor/generator.
2. Description of the Related Art
A U.S. Pat. No. 6,054,776 issued on Apr. 25, 2000 (which corresponds to a Japanese Patent Application First Publication No. Heisei 10-304513 published on Nov. 12, 1998) exemplifies a previously proposed parallel hybrid vehicle, In the previously proposed parallel hybrid vehicle, the torque synthesis mechanism constituted by a differential gear mechanism (planetary gear mechanism) is used to synthesize output torques of the engine and the motor/generator and the synthesized output torque thereat is transmitted via the transmission to driven wheels of the vehicle. A method of starting the parallel hybrid vehicle disclosed in the above-described United States patent is such as to develop a torque from the motor/generator in such a manner that a revolution speed of the motor/generator is made completely or substantially coincident with the revolution speed of the engine while arise in the revolution speed of the engine (also called, engine speed) is suppressed. When the revolution speed of the motor/generator is made completely coincident with or made substantially coincident with the engine speed, a lock-up clutch directly couples the engine and the motor/generator without any interruption. Thereafter, unless a vehicle velocity is reduced, the vehicular driving force from only the engine or from a combination of the engine and the motor/generator is developed.
In the previously proposed parallel hybrid vehicle described above, a regenerative electrical power can be obtained by a regenerative operation for the motor/generator. This regenerative power is changed within a charge device so as to serve as an energy when the motor/generator is used as the motor. In addition, when the motor/generator is in the regenerative operation, a kinetic energy of the vehicle is converted into the regenerative power. Hence, a regenerative driving force is acted upon motor driven wheels drive by the motor/generator. Each of Japanese Patent Application First Publications No. Heisei 8-135762 published on May 31, 1996 (which corresponds to a U.S. Pat. No. 5,771,478 issued on Jun. 23, 1998) and No. Heisei 9-109705 published on Apr. 28, 1997 (which corresponds to a U.S. Pat. No. 5,895,333 issued on Apr. 20, 1999) exemplifies a previously proposed hybrid vehicle drive system with a power regeneration of the motor/generator. In the former Japanese Patent Application First Publication (JP8-135762), a power regenerative drive is carried out with the lock-up clutch maintained at the clutched state until a revolution speed of a carrier of the differential gear mechanism connected to the transmission becomes equal to or lower than a predetermined speed. Hence, since, in an ordinary running region, the motor/generator and the engine are rotated and synthesized together, the kinetic energy of the vehicle consumed in the engine is large during the vehicular deceleration and a sufficient regenerative power cannot be obtained. On the other hand, in the latter Japanese Patent Application First Publication (JP9-109705), a discrete clutch between the carrier of the differential gear mechanism connected to the transmission and the engine is disposed. During the vehicular deceleration, this clutch is released for the engine to be separated so that the energy consumed by the engine is substantially zeroed to improve the regenerative power and a fuel economy can be improved by stopping the separated engine and stopping the supply of the fuel. However, since, in the hybrid vehicle in the latter case, two clutches are needed so that the increase in the number of parts, a mountability (or mounting easiness) on the vehicle, and cost performance become disadvantageous. In addition, when the engine which is stopped is re-started, a complicated control such as a clutch engagement becomes necessary.
It is, hence, an object of the present invention to provide a parallel hybrid vehicle which can obtain a sufficient regenerative power without need of a clutch which cuts off a power between the engine and the differential gear mechanism.
The above-described object can be achieved by providing a hybrid vehicle, comprising: an engine; a charge device; a transmission; a motor/generator having both functions of an electric motor and a generator and carrying out supply and receipt of an electric current to and from the charge device; a differential unit having a first axle connected to an output axle of the engine, a second axle connected to an output axle of the transmission, and a third axle connected to an input axle of the transmission; a clutch interposed between any two of the first, second, and third axles of the differential unit to be engaged when a difference in revolution speed between an engine speed of the engine and a revolution speed of the motor/generator becomes equal to or lower than a predetermined value during a start of the vehicle; and a controlling section that enables controls of an optimum state of the clutch, driving states of the motor/generator and the engine, and gear speed range of the transmission, the controlling section comprising: requested deceleration state estimating section that estimates a requested vehicular deceleration state on the basis of at least one of a vehicular running speed and a brake manipulated variable of a vehicular brake system; a calculating section that calculates the engine speed of the engine, the revolution speed of the motor/generator, and a regenerative power obtained by the motor/generator under both of released and clutched states of the clutch for each gear speed range achievable by the transmission on the basis of the requested vehicular deceleration state estimated by the requested deceleration state estimating section; and an optimum driving state selecting section that selects one of the gear speed ranges of the transmission and the operation state of the clutch on the basis of the engine speed of the engine, the revolution speed of the motor/generator, and the regenerative power obtained by the motor/generator calculated by the calculating section in such a manner that as a charge state of the charge device becomes smaller, the regenerative power obtained by means of the motor/generator becomes larger, the controlling section controlling the operation state of the clutch, the driving states of the engine and motor/generator, and the gear speed range of the transmission on the basis of the gear speed range of the transmission and the clutched state of the clutch related to the driving state selected by the optimum driving state selecting section.
The above-described object can also be achieved by providing a method applicable to a hybrid vehicle, the hybrid vehicle comprising: an engine; a charge device; a transmission; a motor/generator having both functions of an electric motor and a generator and carrying out supply and receipt of an electric current to and from the charge device; a differential unit having a first axle connected to an output axle of the engine, a second axle connected to an output axle of the transmission, and a third axle connected to an input axle of the transmission; a clutch interposed between any two of the first, second, and third axles of the differential unit to be engaged when a difference in revolution speed between an engine speed of the engine and a revolution speed of the motor/generator becomes equal to or lower than a predetermined value during a start of the vehicle; and a controlling section that enables controls of an optimum state of the clutch, driving states of the motor/generator and the engine, and gear speed range of the transmission, the method comprising: estimating a requested vehicular deceleration state on the basis of at least one of a vehicular running speed and a brake manipulated variable of a vehicular brake system; calculating the engine speed of the engine, the revolution speed of the motor/generator, and a regenerative power obtained by the motor/generator under both of released and clutched states of the clutch for each gear speed range achievable by the transmission on the basis of the estimated requested vehicular deceleration state; and selecting one of the gear speed ranges of the transmission and the operation state of the clutch on the basis of the engine speed of the engine, the revolution speed of the motor/generator, and the regenerative power obtained by the motor/generator calculated in such a manner that as a charge state of the charge device becomes smaller, the regenerative power obtained by means of the motor/generator becomes larger, at the controlling step, the operation state of the clutch, the driving states of the engine and motor/generator, and the gear speed range of the transmission being controlled on the basis of the gear speed range of the transmission and the clutched state of the clutch related to the selected driving state.
This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features.